AUTUNITE & META-AUTUNITE
Autunite and meta-autunite are radioactive,
yellowish to yellowish-green, uranium-bearing minerals. They are both
hydrous calcium uranyl phosphate minerals - autunite is Ca(UO2)2(PO4)2·11H2O
and meta-autunite is Ca(UO2)2(PO4)2·6-8H2O.
Autunite
is an alteration product of other uranium minerals and typically occurs in
hydrothermal veins and pegmatitic granites. It has a nonmetallic, glassy
to pearly luster, varies from pale yellow to yellow to greenish yellow to pale
green to dark green to greenish black, has a yellowish streak, is soft (H=2 to
2.5), and has 3 cleavage planes, one of which is perfect (micaceous) and two of
which are poor. Autunite crystals are tabular in shape, having squarish
to rectangular to 8-sided outlines, and range from transparent to translucent
to opaque. Many autunite specimens are finely-crystalline aggregates or
microcrystalline crusts. Thin crystals and thin cleavage fragments are
flexible (elastic). Autunite fluoresces under ultraviolet (UV) light.
Meta-autunite is a more stable, partial-dehydration product of autunite, and many
"autunite" specimens are likely meta-autunite. Meta-autunite
has a nonmetallic, glassy to pearly to dull luster, a bright yellow to greenish
yellow color, yellowish streak, is soft (H=2 to 2.5), and has one perfect
cleavage (micaceous). Unlike autunite, thin crystals and cleavage
fragments of meta-autunite are brittle, not flexible. Meta-autunite
crystals are tabular squares to pseudocubes to pseudomorphs of autunite.
Finely-crystalline to microcrystalline crusts are common. Meta-autunite
is also fluorescent under UV light.
Autunite
(above & below) from Autun, France (Colorado School of Mines Geology Museum
public display, Golden, Colorado, USA).
Meta-autunite from Margnac, Limousin, France (CSM # 69.145, Colorado School of Mines
Geology Museum, Golden, Colorado, USA).
Photo gallery of
meta-autunite